A natural oil-and-fat, mixture of natural oils-and-fats, hydrogenated oil thereof or interesterified oil thereof is a mixture of various triglycerides having different melting point. An oil-and-fat is used for various applications, such as oil-and-fat for deep-frying, oil-and-fat for margarine/shortening, oil-and-fat for filling and oil-and-fat for chocolate, in accordance with physical properties thereof. As a processing technique for adjusting physical properties of an oil-and-fat, oil-and-fat fractionation such as dry fractionation and solvent fractionation has widely been put into practice use.
The above-described solvent fractionation has been traditionally used suitably for fractionation into a crystal fraction and a liquid fraction. However, it is necessary to use hexane or acetone, which is an organic solvent, in a large amount. In recent years, therefore, dry fractionation method which is simpler and higher-in-safety has been widely considered from the viewpoint of safety and relief.
The dry fractionation method is generally a method of cooling a raw material oil-and-fat, which has been completely molten by heating without using any solvent, with stirring in a crystallization tank, thereby precipitating a crystal (crystallization), and then separating the oil-and-fat into a crystal fraction and a filtrate (unsolidified low melting point fraction) by pressing and/or filtration. This method has been already and widely used for fractionation of palm kernel oil, butter oil, palm oil and the like.
The dry fractionation method is a more preferred method than the solvent fractionation also from the viewpoint of energy efficiency. However, as compared with the solvent fractionation, the dry fractionation method is lower in separation accuracy into a crystal fraction and a liquid fraction, and also has problems that the liquid fraction involved in the crystal fraction is not easily removed, and that the crystal slurry rises in viscosity so that the crystal is not easily separated by pressing or filtration when the amount of the crystal is too large after the crystallization.